title: Quaternary ammonium-type gemini surfactants synthesized from oleic acid: aqueous solution properties and adsorption characteristics.
abstract: Cationic gemini surfactants having a quaternary ammonium headgroup have been synthesized from oleic acid. The hydrocarbon chain is covalently bound to the terminal carbonyl group of oleic acid via an amide bond, while the quaternary ammonium headgroup is introduced onto the cis double bond of oleic acid. The Krafft temperature of these surfactants drops below room temperature (ca. 25°C) when the counterion is exchanged from Br⁻ to Cl⁻. The aqueous solution properties of the Cl series of surfactants have been assessed by means of pyrene fluorescence, dynamic light scattering (DLS), and static surface tension measurements. An increased hydrocarbon chain length results in a lower critical micelle concentration (cmc) and a higher adsorption efficiency at the air/aqueous solution interface. Surface tension measurements suggest the formation of premicelles at concentrations below cmc, whereas, above cmc, DLS indicates the formation of micellar aggregates whose diameter ranges from 5 to 10 nm. We, furthermore, characterized the adsorption of these surfactants to the silica/aqueous solution interface and observed their spontaneous adsorption to the solid surface by electrostatic and intermolecular hydrophobic interactions. The combination of soft-contact imaging atomic force microscopy (AFM) and force-curve data suggests bilayer formation above cmc, which is reflective of the large packing parameter of the gemini surfactants. Interestingly, we found the repulsive interaction observed during compression of the adsorbed layer to be relatively weak, as a result of the low adsorption density and/or the loose molecular packing arrangement, which arises from the asymmetric structure.
authors.affiliation: Department of Pure and Applied Chemistry in Faculty of Science and Technology and Research Institute for Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan. k-sakai@rs.noda.tus.ac.jp
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Yuki
authors.initials: Y
authors.lastname: Saito
authors.forename: Akihito
authors.initials: A
authors.lastname: Uka
authors.forename: Wataru
authors.initials: W
authors.lastname: Matsuda
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takamatsu
authors.forename: Boonyarach
authors.initials: B
authors.lastname: Kitiyanan
authors.forename: Takeshi
authors.initials: T
authors.lastname: Endo
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
mesh_terms: D000327:Adsorption; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D019301:Oleic Acid / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D055672:Static Electricity; D013501:Surface-Active Agents / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D008823:Micelles; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D019301:Oleic Acid; D012822:Silicon Dioxide